1. Field
One embodiment of the invention relates to a storage medium such as an optical disk, a reproducing method, and a recording method of the storage medium capable of recording and reproducing information.
2. Description of the Related Art
As write-once type optical disks using an organic dye material for a recording material, there have been commercially available: a CD-R disk using a recording/reproducing laser light with a wavelength of 780 nm; and a DVD-R disk using a recording/reproducing laser light with a wavelength of 650 nm. There has been proposed that a cyanine dye thin film capable of changing physical property with light of a comparatively long wavelength, 790 nm for example, is used for a recording layer (Jpn. Pat. Appln. KOKOKU Publication No. 6-43147, for example.)
On the other hand, in principle, density can be increased in inverse proportion to a square of a recording/reproducing laser light wavelength, and thus, it is desirable that a laser light with a shorter wavelength be used for recording/reproduction. In recent years, there has been developed a next generation optical disk which achieves high density. Here, it is assumed that the wavelength of a recording or reproducing laser light is in the vicinity of 405 nm (namely, in the range of 355 nm to 455 nm). In an organic dye recording material optimized with light of 650 nm in wavelength, if the wavelength of a light to be used becomes shorter than 620 nm, recording/reproducing characteristics drastically change. Thus, an organic dye material which is suitable for a light with a wavelength of 620 nm cannot be used as a recording material for a next generation optical disk.
The above document relates to an information storage medium having a recording layer which contains a cyanine dye. As described in column 7, a wavelength of a recording laser light is 780 nm, and recording using a light with a wavelength of 620 nm or less (particularly from 355 to 455 nm) is not disclosed.
As described above, a conventional information storage medium using an organic dye material has a disadvantage that it cannot carry out recording/reproduction with light of 620 nm or less in wavelength.